Conservative bankroller Michael Ashcroft has finally admitted he is a non-dom, after years of evading the question.
The Tory deputy chairman suggested in a statement released on his website he would give up his non-domicile status if the Tories win the election.
It came after years of resistance to revealing his residency status in public. Lord Ashcroft spends much of time, and bases many of his extensive business interests, in the Central American state of Belize.
Matters came to a head after information commissioner Christopher Graham gave the Cabinet Office just 35 days to end the secrecy surrounding his tax status on February 1st.
Critics had suggested it is wrong that a 'non-dom' wields such significant influence over British politics. Lord Ashcroft has funded a series of targeted campaigns in marginal constituencies which many observers believe could have a decisive impact on the result of the general election.
"As for the future, while the non-dom status will continue for many people in business or public life, David Cameron has said that anyone sitting in the legislature - Lords or Commons - must be treated as resident and domiciled in the UK for tax purposes," Lord Ashcroft said in the statement.
"I agree with this change and expect to be sitting in the House of Lords for many years to come."
Lord Ashcroft confirmed his "precise tax status" was "that of a non-dom".
David Cameron welcomed Lord Ashcroft's decision to reveal his status today, saying: "I'm glad this is cleared up and now we can get on with the election campaign."
He was awarded a life peerage in 2000. Explaining his tax status in a March 2000 memorandum to then-Tory leader William Hague, he said he "intended to take up permanent residence in the UK again".
But this had been officially interpreted to mean being "a long-term resident" of the UK, he stressed.
The Liberal Democrats said the revelation showed the Tories had been "bought like a banana republic".
Home affairs spokesman Chris Huhne said: "The Conservatives' biggest donor is a tax-dodger from Belize who has not paid a penny of British tax on the vast bulk of his estimated £1.1 billion fortune held offshore.
"This raises extraordinary questions about the judgement of successive Tory leaders - William Hague, Michael Howard and David Cameron - whose view seems to be that only little people should pay tax."
There was anger from other opposition parties. SNP constitutional affairs spokesman Pete Wishart said the Tory party should be "ashamed".
"It says a great deal that it has taken years to wring this admission out of the Tories. They are obviously, quite rightly, ashamed of this revelation which directly contradicts their public position," he said.
"The Conservatives can pretend to be a progressive party of change but this admission shows they are just the same old Tories: out of touch and out of favour."
Justice secretary Jack Straw followed a similar tack.
"Instead of paying tax in the UK on all his earned income, he has been channelling millions into the Conservative party to help them buy this election," he said.
"This is precisely what you'd expect from the old Tory party of the 80s and 90s. It just goes to show that rather than having really changed his party, David Cameron has kept it as it was.
Democratisation activists came down hard on the Tories, with Unlock Democracy branding Lord Ashcroft "Lord Loophole of Party Funding".
"This statement confirms that, whilst not technically breaking the agreements he made, he is clearly acting against the spirit in which they were made," said director Peter Facey.
"We wager the average man on the street's definition of 'permanent residence' differs greatly from that which has been agreed in a Whitehall backroom."
Lord Ashcroft claimed he had been motivated to release the information because he did not want it to overshadow the Tories' attempt to win power in the coming general election.
He pointed out two of Labour's biggest donors, Lord Paul and Sir Ronald Cohen, are also 'non-doms'.
Lord Ashcroft has been out of favour in Belize for some time now, with the country's new prime minister, Dean Barrow, saying his government was in a "state of war" with the billionaire.
During a Commonwealth heads of government summit in Trinidad and Tobago last year, Mr Barrow said Lord Ashcroft's position in the British government should the Tories win power could trigger a diplomatic spat between Britain and Belize, which only gained independence from the UK in 1981.
"It's not for me to presume to advise Mr Cameron," he is reported to have said.
"All I can do is to say that I would hope that a practical problem would be managed in such a way as not to damage relations between Belize and the UK."